When formulating new catalysts, a large number of candidate catalyst compositions are typically synthesized. It then becomes important to evaluate the various candidate catalysts to determine and identify those formulations that are the most successful in catalyzing a particularly desired reaction under a selected set of reaction conditions. Activity and selectivity are two key characteristics of a catalyst that are commonly determinative of the success or desirability of the catalyst. The term “activity” commonly refers to the rate of conversion of reactants by a given amount of catalyst under specified conditions. The term “selectivity” commonly refers to the degree to which a given catalyst favors one reaction compared with other possible reactions. From the activity and selectivity values for a given catalyst, yields may be calculated. Thus, it is typically advantageous to evaluate or compare the performance of various catalyst materials based on the activity, selectivity and/or yield achieved with the various catalyst materials.
Traditionally, the activity, selectivity, and yield performance of a catalyst have been evaluated using a sequential approach. In such an approach, each catalyst sample or candidate is typically independently serially tested in a selected reactor at one or more sets of specified reaction conditions. In practice, suitable test reactors for particular applications may take various forms such as micro, pilot, bench-top and lab-scale reactors, for example. In most cases, such a test reactor is operated in a fixed bed mode. Alternatively, when the ultimate envisioned end use of a catalyst is in a fluidized bed application, catalyst samples may be tested using a test reactor operated in a fluidized bed mode. After completion of the tests at one or more sets of conditions, the tested catalyst sample is typically removed from the test reactor and the next catalyst sample is loaded into the respective reactor. The testing is then repeated on the freshly loaded catalyst sample. The process is repeated sequentially for each of the desired catalyst formulations. As will be appreciated, the application of such a process to the testing of numerous various catalyst formulations can be undesirably time-consuming.
Developments in combinatorial chemistry were at first largely concentrated on the synthesis of chemical compounds. Recently, combinatorial approaches have been applied to the testing of catalysts in an effort to expedite the catalyst evaluation process. The use of combinatorial approaches to catalyst evaluation has, however, been generally limited or restricted such as due to difficulties or an inability of ensuring the generation of a self-consistent combinatorial data set. In particular, combinatorial testing in which library members are evaluated at different space velocities typically results in data sets which are not self-consistent, e.g., performance differences may be at least in part attributable to differences in space velocities rather than to differences in the formulation of the various catalyst samples. For example, because a combinatorial approach commonly involves the loading of many samples for each run, the process of individually measuring out a specified weight for each sample can become extremely burdensome. Moreover, because combinatorial synthesis generally produces or results in a wide variety of materials such as may have widely varying properties, such as density, even reactors wherein materials have been loaded in a constant volume manner may contain significantly varying weights of material.
In view thereof, there is a need and a demand for procedural developments in combinatorial catalyst evaluation such as to better ensure self-consistent data sets such as by permitting or facilitating evaluation or comparison of each of multiple catalyst samples at a substantially identical space velocity. Further, there is a need and a demand for an assembly which facilitates and permits the generation of a self-consistent catalyst evaluation data set such as wherein each of multiple catalyst samples is concurrently evaluated at a substantially identical space velocity.